• Tribology and Lubricants
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• 제17권3호
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• pp.171-178
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• 2001

In order to elucidate the lubricating mechanism of polyolester base oils [POEs], the wear characteristics of 27 kinds of polyolester base oils including mixed POEs were investigated. Their wear results were discussed in terms of the effect of molecular structure on wear performance and compared with those of mineral oil. In addition, the adsorption ability of POEs to reduced iron and their hydrolysis rates were measured and the effect of their molecular structures on the adsorptivity and hydrolysis rate of POEs was discussed, respectively. Finally, the lubricating mechanism anlyzed from these results of wear characteristics, adsorptivity and hydrolysis rate was proposed. That is to say, POEs are firstly adsorbed to friction surface and decomposed by hydrolysis or thermal degradation. Fatty acids obtained by degradation of POEs form adsorption film on friction surface. The larger become cohesive ability among fatty acid molecules in the adsorption film, the better gets the wear performance of POEs.

• Elastomers and Composites
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• 제55권2호
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• pp.128-136
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• 2020

The hydrolysis mechanisms as well as the hydrolysis measurement technique and its practical applications in material manufacturing fields are revised. This chapter, Part 1, elaborates the theoretical aspects of the hydrolysis mechanism. Acid-catalyzed and base-catalyzed hydrolysis mechanisms are reviewed. The quantitative analysis method based on the SIM technique using py-GC-MS is reviewed. Examples of hydrolysis of alkoxysilane in elastomer composites currently used in the industry and hydrolysis of amine in plastic composites are shown. Moreover, Part 2 discusses the mechanical property changes in elastomer and plastic composites after hydrolysis.

• Bulletin of the Korean Chemical Society
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• 제20권10호
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• pp.1213-1217
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• 1999

Hydrolysis reactions of 2-phenyl-4H,5H,6H-3-methyl-3-thiazinium perchlorate (PTP) and its derivatives at various pH have been investigated kinetically. The hydrolysis is quantitative, producing N-3-mercaptopropyl-N-methylbenzamide as the only product in the all pH ranges. The observed rate of hydrolysis of PTP was always of the first-order. For hydrolysis from PTP, Hammett ρvalues were 0.53, 0.84 and 1.13 for pH 5.0, 8.0, and 10.0, respectively. Bronsted βvalue was 0.53 for general base catalysis. This reaction is catalyzed by general w acetate concentration. However, as the amount of base becomes larger, the rate of hydrolysis reaction approaches the limiting values. The plot of log k vs. pH shows that the rate constants (kt) are two different regions in the profile; one part is directly proportional to hydroxide ion concentration and the other is not. On the bases of these result, the plausible hydrolysis mechanism and a reaction equation were proposed: Below pH 4.5, the hydrolysis was initiated by the addition of water to α-carbon. Above pH 9.0, the hydrolysis was proceeded by the addition of hydroxide ion to α-carbon. However, in the range of pH 4.5-8.0, these two reactions occured competitively.

• Bulletin of the Korean Chemical Society
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• 제24권1호
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• pp.65-69
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• 2003

The kinetic and chemical mechanisms of AChE-catalyzed hydrolysis of short-chain thiocholine esters are relatively well documented. Up to propanoylthiocholine (PrTCh) the chemical mechanism is general acid-base catalysis by the active site catalytic triad. The chemical mechanism for the enzyme-catalyzed butyrylthiocholine(BuTCh) hydrolysis shifts to a parallel mechanism in which general base catalysis by E199 of direct water attack to the carbonyl carbon of the substrate. [Selwood, T., et al. J. Am. Chem. Soc. 1993, 115, 10477- 10482] The long chain thiocholine esters such as hexanoylthiocholine (HexTCh), heptanoylthiocholine (HepTCh), and octanoylthiocholine (OcTCh) are hydrolyzed by electric eel acetylcholinesterase (AChE). The kinetic parameters are determined to show that these compounds have a lower Michaelis constant than BuTCh and the pH-rate profile showed that the mechanism is similar to that of BuTCh hydrolysis. The solvent isotope effect and proton inventory of AChE-catalyzed hydrolysis of HexTCh showed that one proton transfer is involved in the transition state of the acylation stage. The relationship between the dipole moment and the Michaelis constant of the long chain thiocholine esters showed that the dipole moment is the most important factor for the binding of a substrate to the enzyme active site.

• 한국응용과학기술학회지
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• 제15권2호
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• pp.1-9
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• 1998

The rate constants of hydrolysis of N-tert-butyl-${\alpha}$-phenylnitrone and its derivatives have been determined by UV spectrophotometry at $25^{\circ}C$ and a rate equation which can be applied over a wide pH range was obtained. On the basis of rate equations derived and judging from the hydrolysis products obtained and general base and substituent effects, plausible mechanism of hydrolysis in various pH range have been proposed. Below pH 4.5, the hydrolysis was initiated by the protonation and followed by the addition of water to ${\alpha}-carbon$. Above pH 10.0, the hydrolysis was proceeded by the addition of hydroxides ion to ${\alpha}-carbon$. In the range of 4.5${\sim}$10.0 the addition of water to nitrone was rate controlling step.

• Bulletin of the Korean Chemical Society
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• 제12권3호
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• pp.273-276
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• 1991

The rate constants of hydrolysis of ${\alpha}$, N-diphenylnitrone and its derivatives have been determined by UV spectrophotometry from pH 2.0 to 13.5, and a rate equation which can be applied over a wide pH range was obtained. On the basis of rate equation, hydrolysis product, and general base and substituent effects, a plausible mechanism of hydrolysis has been proposed: Below pH 5, the hydrolysis was initiated by the protonation and followed by the addition of water to ${\alpha}$-carbon. However, above pH 11, the hydrolysis was proceeded by the addition of hydroxide ion to ${\alpha}$-carbon. In the range of pH 5-11, the addition of water to nitrone is rate controlling step.

• Bulletin of the Korean Chemical Society
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• 제24권3호
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• pp.306-310
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• 2003

Hydrolysis reactions of S-phenyl-S-vinyl-N-p-tosylsulfilimine (VSI) and its derivatives at various pH have been investigated kinetically. The hydrolysis reactions produced phenylvinylsulfoxide and p-toluene sulfonamide as the products. The reactions are first order and Hammett ρ values for pH 1.0, 6.0, and 11.0 are 0.82, 0.45, and 0.57, respectively. This reaction is not catalyzed by general base. The plot of k vs pH shows that there are three different regions of the rate constants $(k_t)$ in the profile.; At pH < 2 and pH > 10, the rate constants are directly proportional to the concentrations of hydronium and hydroxide ion catalyzed reactions, respectively. The rate constant remains nearly the same at 2 < pH < 10. On the bases of these results, the plausible hydrolysis mechanism and a rate equation have been proposed: At pH < 2.0, the reaction proceeds via the addition of water molecule to sulfur after protonation at the nitrogen atom of the sulfilimine, whereas at pH > 10.0, the reaction proceeds by the addition of hydroxide ion to sulfur directly. In the range of pH 2.0-10.0, the addition of water to sulfur of sulfilimine appears to be the rate controlling step.

• 한국응용과학기술학회지
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• 제9권2호
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• pp.119-126
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• 1992

The kinetics of the hydrolysis of indolylacrylophenone derivatives(IA) was investigated by ultraviolet spectrophotometry in 30% dioxane-$H_2O$ at 25$^{\circ}C$ Rate equations were obtained over a wide pH range. On the basis of rate equation, general base catalysis and Hammett's plot, the mechanism of hydrolysis to the (IA) were proposed: Below pH 3.0, the hydrolysis of (IA) was proportional to hydronium ion concentration, between pH 4.0${\sim}$9.0 neutral water molecule and hydroxide ion were added to carbon-carbon double bond and over pH 10.0 hydrolysis of (IA) was proportional to hydroxide ion concentration.

• Applied Biological Chemistry
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• 제38권5호
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• pp.455-462
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• 1995

새로운 6종의 제초성, N-(2,6-dimethoxypyrimidin-2-yl)aminocarbonyl-2-치환(Z)-6-(1-hyd roxy-2-fluoroethyl)benzenesulfonamide 유도체(S)를 합성하여 $45^{\circ}C$의 15%(v/v) acetonitrile 수용액속에서 일어나는 가수분해 반응상수를 측정하고 pH-효과, 용매효과, ortho-치환기 효과, 열 역학적 활성화 파라미터(${\Delta}H^{\neq}$및${\Delta}S^{\neq}$) 등의 반응 속도론적인 자료들과 pKa상수(4.80) 및 가수분해 반응 생성물(2-(1-hydroxy-2-fluoroethyl)benzenesulfonamide 및 4,6-dimethoxyaminopyrimidine) 분석 등의 비 반응 속도론적 결과로부터 반응속도식을 유도하고 반응메카니즘을 제안하였다. pH 8.0 이하에서는 일반 산-촉매반응($A-S_E2$)과 특정 산-촉매 반응으로 conjugate acid ($SH^+$)와 사면체 중간체(I)를 경유하는 A-2형(또는 $A_{AC}2$형)반응 그리고 pH 9.0 이상에서는 물 분자가 일반염기(B)로 작용하여 conjugate base (CB)를 경유하는 $(E_1)_{anion}$ 반응으로 진행되는 가수분해 반응 메카니즘을 검토하였으며 pH $7.0{\sim}9.0$사이의 용액중에서는 이들 두 반응이 경쟁적으로 일어남을 알았다.

• 한국환경과학회지
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• 제17권5호
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• pp.509-516
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• 2008

New functional surfactant, N,N-dimethyl-N-dodecyl-N-(2-methyl benzimidazoyl) ammonium chloride(DDBAC) having benzimidazole(BI) functional group have been synthesized and the critical micellar concentration of DDBAC measured by surface tentiometry and electric conductivity method was $8.9{\times}10^{-4}M$. Micellar effects in DDBAC functional surfactant solution on the hydrolysis of p-nitrophenylacetate(p-NPA), p-nitro-phenylpropionate(p-NPP) and p-nitrophenylvalerate(p-NPV) were observed with change of various pH (Tris-buffer). The pseudo first rate constants of hydrolysis of p-NPA, p-NPP and p-NPV in optimum concentration of DDBAC solution increase to about 160, 280 and 600 times, respectively, as compared with those of aqueous solution at pH 8.00(Tris-buffer). It is considered that benzimidazole functional moiety accelerates the reaction rates of hydrolysis because they act as nucleophile or general base. In optimum concentration of DDBAC solution, the rate constants of hydrolysis of p-NPP and p-NPV increase to about 1.5 and 3.0 times, respectively, as compared with that of p-NPA. It means that the more the carbon numbers of alkyl group of substrates, the larger the binding constants between DDBAC micelle and substrates are. To know the hydrolysis mechanism of p-NPCE(p-NPA, p-NPP and p-NPV), the deuterium kinetic isotope effects were measured in $D_2O$ solutions. Consequently the pseudo first order rate constant ratios in $H_2O$ and $D_2O$ solution, $k_{H_2O}/k_{D_2O}$, were about $2.8{\sim}3.0$ range. It means that the mechanism of hydrolysis were proceeded by nucleophile and general base attack in approximately same value.